Optical packet switching is an attractive technology that enables more effective and flexible utilization of the capacity of WDM optical networks by providing sub-wavelength granularity. Optical-label switching, as one of the promising packet switching schemes, offers several key features that are important to future data-intensive networks. These features include protocol and format independent transparency at the all-optical data plane, simplification in the control plane, and interoperability with legacy and emerging networking technologies including GMPLS. Such a switching scheme is discussed in D. J. Blumenthal, et al., “All-Optical Label Swapping Networks and Technologies”, Journal of Lightwave Technologies, Vol. 18, No. 12, pp. 2058-2075 (2000), which is incorporated herein by reference.
Optical-label packet transmission schemes have been proposed in which a packet payload is carried using amplitude-shift-keying (ASK) modulation and the packet label is carried using differential-phase-shift-keying (DPSK) modulation. Such an optical label generation scheme is discussed in N. Chi et al., “Transmission and Transparent Wavelength Conversion of an Optically Labeled Signal Using ASK/DPSK Orthogonal Modulation”, IEEE Photonics Technology Letters, Vol. 15, pp. 760-762 (2003), which is incorporated herein by reference. Receiver sensitivities with an optical pre-amplifier (at BER=10−9) of ˜−26 dBm and −30 dBm were obtained for a 10-Gb/s ASK payload and a 2.5-Gb/s DPSK label, respectively.
Prior art schemes, such as the one proposed by N. Chi et al., which use DPSK modulation to carry the low-speed label information and ASK to carry the high-speed payload information, have a number of drawbacks. First, since DPSK modulation is used to carry low-speed label information, the delay interferometer, needed in DPSK demodulation, has a long delay difference between the two arms of the delay interferometer, and thus, it is very temperature sensitive and polarization sensitive. Secondly, any change in the data rate of the label requires a change of the delay interferometer (to obtain a matched delay). Thirdly, the removal and insertion of packet labels is difficult since the label is phase modulated. To remove a label, Chi et al. propose the use of cross-gain modulation, which will change the signal wavelength. This is not be desirable for cases where signal wavelength needs to be maintained. To add a label, expensive phase-sensitive modulation is required. Finally, low-speed DPSK requires a high-coherence (low bandwidth) source (CW) laser and is less tolerant to nonlinear effects such as cross-phase-modulation (XPM).